I already downloaded and installed Oracle 11g release 2 32-bit for windows 7
(i used 32-bit oracle installer for my 64-bit windows 7 because the 64-bit installer can't install succesfully)
After that i opened SQL Plus, and it asks me for username and password but i don't have it.
Can you guys help me with this? Do you know some username/password that i can use?

anyway i installed ORACLE 11g database for studying purposes.
and i follwed the instructions here: http://www.tutorialspoint.com/plsql/plsql_environment_setup.htm

I already downloaded and installed Oracle 11g release 2 32-bit for windows 7
(i used 32-bit oracle installer for my 64-bit windows 7 because the 64-bit installer can't install succesfully)
After that i opened SQL Plus, and it asks me for username and password but i don't have it.
Can you guys help me with this? Do you know some username/password that i can use?

In the link you have mentioned - when are you in Step 5 - what is the Adminstrative Password you have given..? - Use that password to connect to sys - Later unlock scott user like - alter user scott account unlock